bash Shell 脚本按空格分割字符串
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Shell script split a string by space
提问by Jes
The bash shell script can split a given string by space into a 1D array.
bash shell 脚本可以将给定的字符串按空格拆分为一维数组。
str="a b c d e"
arr=($str)
# arr[0] is a, arr[1] is b, etc. arr is now an array, but what is the magic behind?
But, what exactly happened when we can arr=($str)? My understanding is the parenthesis here creates a subshell, but what happen after that?
但是，当我们可以的时候究竟发生了什么arr=($str)？我的理解是这里的括号创建了一个子shell，但之后会发生什么？
回答by chepner
In an assignment, the parentheses simply indicate that an array is being created; this is independent of the use of parentheses as a compound command.
在赋值中，括号只是表示正在创建一个数组；这与括号作为复合命令的使用无关。
This isn't the recommended way to split a string, though. Suppose you have the string
但是，这不是拆分字符串的推荐方法。假设你有字符串
str="a * b"
arr=($str)
When $stris expanded, the value undergoes both word-splitting (which is what allows the array to have multiple elements) and pathname expansion. Your array will now have aas its first element, bas its last element, but one or more elements in between, depending on how many files in the current working directly *matches. A better solution is to use the readcommand.
当$str膨胀时，值既经历字分裂（这是允许阵列具有多个元素）和路径扩展。您的数组现在将a作为它的第一个元素，b作为它的最后一个元素，但中间有一个或多个元素，具体取决于当前工作中直接*匹配的文件数量。更好的解决方案是使用该read命令。
read -ra arr <<< "$str"
Now the readcommand itself splits the value of $strwithout also applying pathname expansion to the result.
现在，read命令本身会拆分 的值，$str而不会对结果应用路径名扩展。
回答by sjsam
It seems you've confused
看来你糊涂了
arr=($str) # An array is created with word-splitted str
with
和
(some command) # executing some command in a subshell
Note that
注意
arr=($str)is different from arr=("$str")in that in the latter, the double quotes prevents word splitting ie the array will contain only one value -> a b c d e.
arr=($str)不同于arr=("$str")在于：在后者中，双引号防止字分裂即阵列将仅包含一个值- > a b c d e。
You can check the difference between the two by the below
您可以通过以下方式检查两者之间的区别
echo "${#arr[@]}"
